Perhaps both hands, but at highway speeds I only use one, and I use AS all the time on highways. At speed it doesn't take much steering angle to avoid an obstacle, and for me, holding the wheel around 8 or 4 o'clock position depending on which hand, coupled with lightly gripping the wheel while occasionally gripping slightly firmer to satisfy the nag timer works well.
Here is the point I think most people are missing about the "hands on the wheel policy." Admittedly it took me a long time to come around but with 107,000 miles on my 2015 70D, the vast majority on AP, I have had plenty of time to come to this conclusion.
Originally I was under the impression (like most on this thread) that hands on the wheel is a poor proxy for paying attention. Just because you are holding the wheel doesn't mean you are paying attention; conversely, it is possible to be paying attention without touching the wheel.
Nag frequency is inversely proportional to autosteer path confidence. Wide-open multi-lane well-mapped clearly-lined divided highways have the least frequent nags; as confidence decreases (more traffic, curves, construction, etc.) the frequency of nags goes up. No surprise here. As confidence goes down, there is less time to react to an autosteer error (e.g., traffic nearby, in a curve).
I am suggesting that the need for hands on the wheel is more to reduce reaction time than to gauge attentiveness. As an example, I can be driving down the highway with my hand on the wheel, and become distracted (well, not ME of course...only other people). However, I will immediately notice when the wheel starts to do something I don't expect it to. This will grab my attention and I can take immediate action. The tactile feedback path is almost immediate. On the other hand, if I am sitting there, eyes glued to the road but hands on my lap, if I see the car make an incorrect move, I first have to take note of it, move my hands to the wheel, and finally take corrective action. This additional amount of time might not be sufficient in a low-confidence situation, like riding between two trucks.
So, do I like the nags? No, but now I see why holding the wheel is an effective feedback mechanism when autosteer starts to go awry.